Best DNA extraction method from BAL-supernatant

Looking for recommedations on the best method to extract DNA from
bronchoalveolar lavage( BAL) supernatant.
I am doing research on P.carinii. At my hospital we have a large bank
of BAL's , however as some of the cell pellets already have been used
for other purposes, in some instances the only material we have left is
supernatant. Originally BAL's ( 20-30 ml) was spun at 500G for 10 min
and supernatant (approximately 10 ml) saved at -20C and -80C.
I have tried doing simple ethanol precipitation on the supernatants and
tried a BIO 101 GNOME DNA isolation kit- but by both methods the yield
is low and PCR too often negative.
Anybody know better methods for extracting ( a probably tiny amount) of
DNA from this material???
Thanks
Jannik Helweg-Larsen
Dept Of Infectious diseases 144
2650 Hvidovre Hospital
Denmark
e-mail: xxjhelweg at inet.uni2.dk
( remove xx---)